I like what you've done so far, but the dithering is somewhat distracting. Cars have smooth surfaces, while the dithering suggests texture.
The color ramps are a bit boring at the moment, since they go straight to black without any variation in hue. A bit of blue in the darker shades makes the palette a bit more interesting. You can also throw out some of the similar shades and lower the color count a bit.
I'd also try not to use black outlines for everything. In between brighter colors, you can use lighter shades. Otherwise, the lines will seem very thick.
Hope that helps.